This application relates generally to gas turbine engines and, more particularly, to control systems for gas turbine engine.
Because an amount of thrust produced by an aircraft engine can not be measured in flight, gas turbine engines typically use control systems that indirectly control thrust by controlling engine fan speed or engine pressure ratio. Specifically, such control systems infer engine thrust from parameters that can be measured, such as a rotational speed of a fan or a ratio of nozzle inlet pressure to fan inlet pressure. The measured parameters are compared to power management schedules preloaded into the control systems.
To account for engine-to-engine manufacturing quality variations, deterioration of engine components over time, control sensor measurement errors, and changes in operating conditions, such as humidity, the control systems typically preset each control parameter within the power management schedule at a higher value than is actually needed. As a result, actual thrust produced is at least equal to, but usually higher than, an amount of engine thrust desired.
Because the aircraft engines are not trimmed in real-time, the control systems are pre-programmed to produce a minimum amount of thrust from even a deteriorated engine. Accordingly, engines that have not deteriorated produce more thrust than necessary for a given set of operating parameters. The additional thrust causes the engines to operate with increased operating temperatures. Furthermore, because the schedules do not change with time or in response to specific engine characteristics, such engines may never be trimmmed to produce an optimal desired thrust. Over time, continued operation of the engine at increased temperatures may shorten engine life, increase operating costs, and limit user flexibility in selecting operating ranges for the engine.
In an exemplary embodiment, a control system trims a gas turbine engine in real-time to provide a desired amount of thrust. The control system includes a controller coupled to the engine for receiving inputs from the engine regarding a status of the engine. The controller includes a processor and a memory coupled to the processor. The processor is programmed to execute control logic. An engine power schedule representing values for a controlled variable is stored in the memory.
During operation, the processor uses the engine inputs to determine a commanded fuel flow that corresponds to an amount of thrust desired. Because the control system trims the engine in real-time and does not control the engine using fixed schedules that do not change in response to changing operating characteristics of the engine, on-wing engine life for the engine is increased. Furthermore, because the engine is trimmed in real-time and is not trimmed using schedules that result in producing more thrust than necessary, excess thrust of the engine is reduced and the engine operates with lower operating temperatures, lower operating costs, and more reliability.